In recent years the use of digital cameras, which offer easy processing of digital information that has been photographed, has spread rapidly accompanying the spread of personal computers. More compact, low-cost digital cameras are being sought and, to this end, achieving a more compact, low-cost photographic lens for such a camera is an urgent task.
The photographic lenses disclosed in Japanese Laid-Open Patent Applications H5-157962 and H11-125767 are commonly known lenses that respond to these needs. However, the photographic lenses disclosed in these publications use at least five or six lens components, so further compactness and cost reduction are desired.
Digital cameras use a small electrical image sensor, in contrast to conventional compact cameras that use silver chloride film, and it is necessary in such an image sensor for the primary light rays to be incident substantially orthogonal to the entire image sensor surface. In addition, a high aperture efficiency and a long back focus are also required, and hence the design criteria for photographic lenses of digital cameras are fundamentally quite different from that of compact cameras that use silver chloride film.
The present invention is a single focus lens that is formed of only four lens elements while favorable correcting aberrations, so as to provide a more compact and lower cost single focus lens than is currently available. The single focus lens is for use in a compact, yet low-cost camera, particularly a digital camera.